Topic 7 Weathering

Question 1

Why do rocks weather?

Answer 1

Rocks are not stable under current environmental conditions

Most rocks formed in drastically different environment then they are currently in

Question 2

What are the two main controllers on the type and rate of weathering?

Answer 2

Climate and lithology are the main controls on the type and rate of weathering (e.g. water and temperature)

Question 3

What are the two main types of weathering

Answer 3

Physical weathering and chemical weathering

Question 4

Physical weathering: Disintegration

Answer 4

Prodices smaller particles from larger ones. Rocks break down continuously as stress is exerted

Question 5

Physical weathering: Unloading

Answer 5

Deeply buried rocks are under high pressure. erosion removes overburden, the pressure decreases, and the rock heaves upward. creating slab like rock structures

Question 6

Physical Weathering: Crystallization

Answer 6

ground water carries dissolved salts, salts crystallize and expand as water evaporates, exterts force and rock cracks

Question 7

Physical Weathering: Frost Action

Answer 7

Freezing water leads to ice crystal growth, as the volume increases it creates mechanical force outwards

Question 8

Physical Weathering: Thermal Expansion

Answer 8

Heating= expansion
cooling= contraction
frequent, extreme fluctuations result in rock breaking off

Question 9

Chemical Weathering: Decomposition

Answer 9

Mineral alteration or mineral decomposition - involves chemical reaction.
Involves change in chemical composition of minerals.
Destroys primary (old) minerals
Create new (secondary) minerals

Question 10

Chemical Weathering: Hydration

Answer 10

combination with water (little chemical change)

Question 11

Chemical Weathering: Hydrolosis

Answer 11

chemical reaction with water
Breakdown of water into H+ and OH-
produces new compounds

Question 12

Chemical weathering: Oxidation

Answer 12

Chemical combination with oxygen (e.g. Iron ‘rust’)

Question 13

Chemical weathering: Solution

Answer 13

Mineral dissolves:
forms no new weathering products

Ground water dissolves bedrock

Question 14

Chemical weathering: carbonation

Answer 14

solution in carbonic acid
Carbonic acid= water vapour + carbon dioxide

Question 15

Biological Weathering

Answer 15

Biological activities directly break down rocks (e.g. people, animals and plants)

Example: Roots of woody species exert expansive force as roots enlarge and lengthen